1. The Field of the Invention
The present invention relates to a method for simply removing a low-concentration radioactive substance, a removing material suitable for the method, and a solvent composition for removing.
2. The Relevant Technology
At present, it is considered that materials exposed to radiation in nuclear power plants or the like can be subjected to waste treatment when radioactive substance is removed at a low-concentration level of residual contamination with radioactive substance, where contamination is hardly observed (clearance level). However, since equipment and tools are used under the condition that they are reused, the following methods have been applied: a gentle removal method that does not damage materials; and a method of wiping contaminated parts with a cloth piece moistened with water or a removing agent with little chemical reaction (such as alcohol, acetone, and a synthetic detergent) (refer to Non-Patent Document 1). Even at present, the removal work is done mainly by wiping, for example, with a disposable towel like Kimtowel (manufactured by Nippon Paper Crecia Co., Ltd.) immersed with a 50% by volume aqueous solution of ethanol. However, the current removing material (Kimtowel immersed with a 50% by volume aqueous solution of ethanol) has insufficient removing performance and requires repeated wiping operations. In addition, the cleanliness after wiping depends largely on a worker's impression. Moreover, removing materials can be discarded only after they are dried. Therefore, the use of a disposable towel immersed with a 50% by volume aqueous solution of ethanol, which has poor drying properties, requires drying treatment of a wiped-off surface and the disposable towel before discarded, after wiping. Further, the 50% by volume aqueous solution of ethanol also has a problem against inflammability.    Patent Document 1: Japanese Patent Application Laid-Open No. 5-508418.    Patent Document 2: Japanese Patent No. 3482488.    Patent Document 3: U.S. Pat. No. 5,466,877.    Non-Patent Document 1: “RADIOISOTOPES” magazine, pp. 57-62, vol. 23, No. 12, (1974), issued by the Japan Radioisotope Association.